Polarization is an important property of light ordinarily not detected by the human eye. Whereas insects already for a long time find their way using the sky's scattered polarized light, humans have exploited polarization only lately. Sun glasses specifically suppress the sky's scattered light. Photographers place polarizing filters in front of the camera lens to suppress reflections from glass panes or other surfaces. Streak photography is significant in quality control, for instance rendering visible stresses in a glass bottle. It is also known that the light transmitted through two linear polarization filters depends on the relative rotation between the two filters, the light intensity obeying Malus law of the cos2 of the angle. This law can be applied to measure angles and in display means.
Probably at this time the most important field of application of polarizers is in the display technology. Liquid crystal displays (LCD's) make use of large-area polarization filter sheets with a constant direction of polarization in order to create a change between bright and dark by optical rotation or reversal of orientation in a liquid crystal between two such polarizing filter sheets. Large scale production of polarizing filters is no longer a problem. Such a polarized filter sheet operates on the principle to align for instance long-chain molecules serving as microscopic antennas parallel to each other by mechanical processing (rolling, stretching, rubbing, external electric or magnetic fields) during their manufacture. If light is incident in a manner that the plane of oscillation of the electric field runs parallel to the molecules acting as microantennas, then said light shall cause a current. As a result and depending on the nature of these micro-antennas the light is reflected or absorbed. On the other hand no significant interaction takes place in the transverse direction, and the light is transmitted. Polarization dependence presupposes the distances between the micro-antennas are sufficiently small relatively to the light wavelengths. Illustratively such manufacturing procedures are described in DE 696 01 621 T2 which also discusses the quality and life of such sheets, in DE 690 29 683 T2 and in DE 689 27 986 T2 also describing manufacturing polarizing filters according to pattern. DE 41 14 229 A1 describes industrial, large-scale manufacture of polarizing cast sheets at high manufacturing rates. DE 40 26 892 A1 describes further classes of cast sheets. DBP 1 015 236 describes a manufacturing method allowing extending the polarization into the far infrared. DE 199 33 843 B4 discusses manufacturing LCD's using unstructured polarizing filter sheets, describing therein the lithographic structure of electrode materials.
Manufacturing polarizer details, in particular polarized zones of controlled alignments, is difficult. It is uneconomical to cut into small pieces a polarizing filter sheet and to put it together like parts of a puzzle, and moreover it is not precise enough as regards adjustment tolerances. Nano-technology is still a young branch and relates in part to the manufacture of optical gratings and nano-tubes or nano-wires frequently made of carbon or iron (T. P. Hülser et al, “Self-assembled Iron Nanowires: Morphology, Electrical and Magnetic Properties”, Materials Research Society Symposium Proceedings Vol. 877E, 2005), however controlling the manufacture is far from a simple manner. Moreover problems are encountered when aligning the structures so made. It is uneconomical in the present state of the art to manufacture a micro-array of polarizers with deliberate different orientations. DE 100 26 080 A1 describes a procedure whereby an initially a large-area homogeneously polarized sheet loses its polarizing action at some sites due to selective post-processing, and a procedure of assembling several such sheets into one polarizing filter which is multi-directionally polarizing. Besides damping, the filter weight also increases with each additional layer, and it is difficult to accurately adjust and affix sheets prepared in this manner on a support/substrate. The above document also describes controlling the polymerization of an initial material by irradiating it with polarized light, but qualitatively such polarization is less effective than that obtained by mechanical processing.
There are a number of applications measuring angles of rotation employing an equal number of measurement procedures. A frequently encountered problem is measuring the angles of rotating parts for instance to ascertain the position of a transducer (control stick, pedal etc.) or of a servo.
A servo 300 receives a reference value 304, for instance a predetermined angle, and must convert said default into a mechanical position (FIG. 3). For that purpose this servo is fitted with a sensor 303 and a control circuit 302 appropriately driving the servomotor 301. Conventional servos use a potentiometer for the measurement. This potentiometer is connected to the shaft of a motor or to gearing and allows measuring for instance an angle of rotation. A conventional potentiometer is made of an electrically conducting graphite or an electrically conducting plastic arcuate segment fitted with electrical terminals at both ends. A mechanical wiper makes point contact with the arcuate conducting segment and taps the voltage at its contact point. Depending on the angle of rotation, the potentiometer acts as a voltage divider with a voltage division ideally between 0 and 100% representing a comparison value to the 0 to 100% position information. There is an obvious problem in mechanical wear because said wiper must touch the surface. Also the wiper must be mounted in play-free manner on a shaft. The servo must overcome a frictional force to displace the wiper and this feature may be problematical in miniature servos. Potentiometers again are unsuitable in applications requiring free rotations.
Just as frequently a solution must be found to measure an angle when using a forked light barrier [slotted interrupter] 400 in combination with a slotted stop (aperture) 404 or coding disk (FIG. 4a). Considering that typically only relative changes in position are measured (absolutely coded coding disks are expensive/complex and very laborious in signal detection), the generation of a digital signal for control purposes is not necessarily helpful. The servo's positioning accuracy is determined by the number of slits per revolution on the stop. There are limits on arbitrary increases, because entailing ever increasing adjustment accuracy and the susceptibility to soiling and damage rising markedly. Such limitations may be overcome either by using mechanical gearings or increasing the size of the slotted stop. Both desiderata are impeded by miniaturization and cost reduction. Also there are inductive and capacitive position sensors 411 operating by counting voltage peaks as the gear teeth 410 move past them (FIG. 4b) and thereby they basically also raise the same problems. It is possible to measure angles in analog manner within a limited angular range (only several tens of degrees) by proximity sensing/measuring two different reference positions 502, 503 and a signal generator 501. In this manner the ratio of two inductive or capacitive test values may be converted into a signal related to the position of display element 500 in the manner of a potentiometer, however without mechanical wear and friction (FIG. 5). Again the limitation to narrow angles and the spatial bulk of the test unit conflict with miniaturization. All the above discussed systems incur further drawbacks. Measurement accuracy, i.e. sensor operation, depends on mechanical tolerances. Also, none of the above measurement principles is appropriate at exceedingly high rotational speeds.
Various competing methods are available to reproduce stereoscopic images, such reproduction being one of the applications of the present invention. DE 199 24 096 C2 employs three primary colors (R/G/B) and one holographic screen together with orthogonal polarizers to implement position-independent viewing of a projected stereo image. Optical modulators and phase plates in the light path allowing changing between different planes of polarization. However miniaturizing is feasible only in limited manner in this design. DE 195 10 671 A1 describes an LCD screen able to generate different proportions of orthogonal polarization directions at each pixel. This design employs a kind of double LCD structure, the first structure being dedicated to intensity and color, the second structure to re-orient the polarized light or the proportionate resolution into orthogonal components. However mechanical problems, problems in adjustment and weight are likely in this design even though it is a significant improvement over the three alternatives discussed in this document and in particular being free of a reduction in resolution or in the image rate. Yet this effect is attained not by site-selective polarization filters but by site-selective control of liquid crystals. Controlling this display entails a special computation stage wherein the individual pictures are appropriately superposed. Presumably entirely independent image contents for the left and right eyes or for different observers cause/produce artifacts because of unavailability of independent pixels. Conceivably individual pixels might be driven in fixed, stationary manner to attain a matrix with differently polarized LCD pixels. In that case, on the other hand, the screen resolution would be reduced. Nor is it clear how precisely the second LCD layer is able to rotate the light, that is, how completely the partial images might be separated.